The critical impact of tumor size in predicting cancer special survival for T3aM0M0 renal cell carcinoma: A proposal of an alternative T3aN0M0 stage

OBJECTIVE: Based on the eighth TNM staging system, T3a renal cell carcinoma (RCC) is identified as an anatomical extrarenal invasion and does not consider the size of the tumor; however, it may not fully predict the prognosis of the patient. The objective of this study was to evaluate the prognostic value of tumor size effects on prognosis in T3a RCC and propose an alternative tumor stage system combined with T1‐2. METHODS: Data relating to T1‐3aN0M0 RCC (n = 49586) were obtained from the Surveillance, Epidemiology, and End Results database (2004–2015). Survival analyses were conducted by Cox regression and Fine and Gray regression. Harrell's concordance index (c‐index) was used to assess the discriminatory ability of the prognostic factors. RESULTS: A 1‐cm increase in T3a RCC resulted in an 8% increase in all‐cause mortality (hazard ratio [HR]: 1.08; 95% confidence interval [CI]: 1.06–1.10, p < 0.001) and 14% increase in the risk of RCC‐specific mortality (sub‐distribution HR [sHR]: 1.14; 95% CI: 1.11–1.16, p < 0.001). T3a tumor size stratified by the cutoff of 4 cm and 7 cm showed a better prediction of RCC‐special survival (c‐index: 0.644), compared with a cutoff just by 4 cm (c‐index: 0.571) or by 7 cm (c‐index: 0.602). Compared with T1b tumors, T3a RCC ≤4 cm showed no differences in terms of all‐cause mortality (HR: 0.93; 95% CI: 0.79–1.09; p = 0.37) and mortality caused by RCC (sHR: 0.91; 95% CI: 0.70–1.19; p = 0.50). Last, the alternative T‐staging system (T1a, a combination of T1b and T3a [≤4 cm], T2a, T2b, T3a [4–7 cm], and T3a [>7] cm) demonstrated good RCC‐special survival predictive accuracy (c‐index: 0.729), which was higher than that shown by the current eighth edition T‐staging system (c‐index: 0.720). CONCLUSION: Tumor size should be taken into consideration for T3aN0M0 RCC rather than based on anatomical features alone.